Conventional apparatus for compacting granular molding materials with pressurized gases, particularly compressed air, have a passage opening between its pressure chamber and mold unit covered by a diaphragm or a plate-like shut-off element. The diaphragm or element closes and opens the passage opening to permit the air pressure to contact and compress the molding material.
When the full passage opening is in use in the conventional apparatus, the transverse cross-sectional area of the passage opening determines the force required to lift the packing element. Such packing element can be a diaphragm, a valve disk or some other device. The larger the cross-sectional area of the passage opening, the greater is the required lifting force to open the passage opening.
The greater lifting forces, required for conventional apparatus with large transverse cross-sectional area passage openings, are difficult to attain. This is especially the situation with rapid-opening devices because of the short time available to move the packing element.